There is a substantial need in the moving of bulk cargoes by railway hopper cars for a car which may be used either for bulk cargoes which need protection from weather or those which do not. Many of the bulk cargoes which need protection from weather are food or feed grains, all of which can be loaded into a hopper car from a relatively small filler spout under a grain elevator, so that except for a loading hatchway the top of the car may be closed.
On the other hand, most of the bulk cargoes which do not need to be protected from weather consist of coarser materials such as coal, stone or the like, which cannot be handled through a loading spout and which thus require a completely open top hopper car for loading.
There have been a number of attempts to provide a satisfactory convertible railway hopper car; but insofar as applicant is aware none of them has met with any commercial success. U.S. Pat. Nos. 4,117,126, 1,344,322, and 3,132,600 all disclose railway cars having movable roof panels which, when they are not in position to form a roof over the car and to cover the interior of the car, are pivoted to hang outside the sidewalls of the car. A fundamental problem with all such constructions is that when the roof panels are hanging outside the car sidewalls they necessarily decrease the clearance between the cars; and in order to maximize car capacity most railway freight cars, including hopper cars, are made as wide as railroad clearance regulations permit.
U.S. Pat. No. 2,997,967 illustrates another approach to the problem, with roof sections that roll up at one or both ends of the car, in the manner of a roll-top desk. Any such roll-up roof which is to be structurally strong enough for railroad use produces very large and awkward bundles at the ends of the car when the roof is rolled up, and also requires considerable power to roll it up.
U.S. Pat. No. 3,736,883 discloses a third approach, in which roof panels are hinged on the beams that define the sides of a center loading hatchway, and the roof panels occupy upright positions when they are not laterally extended to cover the car body. In the upright position the panels may cause clearance problems. Insofar as applicant is aware, the Pullman Company, which owns U.S. Pat. No. 3,736,883, has never sold a car embodying the structure of the patent.